In North America, and indeed in most of the civilized and populated areas of the world, roads have become an integral part of cities, towns, suburbs, and so on. Indeed, most towns and cities contain hundreds or thousands of miles of roads within their boundaries, and also driveways or parking lots for virtually every building within a city or town.
The conventional way and indeed the most popular way to provide roads, driveways, and parking lots with a top surface is to use asphalt for the top surface. A best estimate is that several million miles of roads and several million acres of parking lots within North America are surfaced with asphalt.
However, there are two fundamental problems with asphalt. One problem is that asphalt is oil based, or at least largely so, and therefore a raw material that is in limited supply is being used when it could be being used for other purposes. Secondly, there is a question of durability, which is now generally recognized as a very significant problem. Many existing roadways and parking lots, even very new ones, are degraded considerably largely due to broken asphalt, and cracks or potholes can be found at any given time. The amount of asphalt roadway in North America that has asphalt damage is quite extensive. Most of the damage is caused by weather cycles, which cause expansion and contraction of the asphalt. Any roadway that does not have asphalt damage has most likely been constructed or repaired in the last few years. This is generally unsightly and also quite expensive. Further, oil and other fluids that drip from vehicles while the vehicle is parked or in motion also cause a significant problem. The amount of damage that is done by oil and other fluids from vehicles is considerable. This damage can be seen in virtually every parking lot, driveway, and roadway intersection in North America. Not only does the oil, or whatever fluid that might be leaking from a vehicle, leave a very unsightly stain on the asphalt surface of a roadway, parking lot or driveway, the asphalt surface in time will start to degrade to a point where it is crumbling and needs to be replaced.
While it is possible to replace small portions of the asphalt surface, at least in most cases, this leaves an unsightly patch--or indeed several patches--of new asphalt.
One alternative that has been recently fairly widely accepted in Noah America as an alternative for resurfacing driveways and small parking lots is interlocking blocks. Interlocking blocks are made of a cementitious or a cement based material having a small relatively constant sized aggregate therein. These blocks come in various shapes and sizes. Basically, these blocks interfit with one another such that the blocks can be installed on a surface to completely cover the surface. The blocks may need to be cut around the perimeter of a surface in order to fit exactly to the outline of the surface. Among the advantages of interlocking blocks are that they do not require the same heavy equipment to install as it takes to create a surface of asphalt, they are easy to replace, only the damaged blocks need replacing which can be done relatively quickly and inexpensively, and they last much longer than an asphalt surface and are much more resistant to damage--including weathering, impact, and leaking oil. They are, however, more expensive to install initially than an asphalt surface, although the cost factor can be spread over many more years since interlocking blocks are generally much more durable than asphalt. Further, it generally takes longer to install a given area of interlocking blocks than to pave the same area with asphalt, which adds to the initial cost. Largely because of the lower initial cost, many parking lots and driveways are still paved with asphalt instead of being surfaced with interlocking blocks. However, because of the long term cost benefits, it is becoming more and more acceptable to use interlocking blocks even where cost is an important and an accountable factor, such as in municipal roads and parking lots or shopping mall and office complex parking lots.
Another advantage of interlocking blocks is that they can, in most cases, allow for ground movement without breaking. The blocks merely shift slightly with respect to one another or in some cases separate slightly :from one another, which is usually acceptable. Further, moisture can pass between interlocking blocks which means that normal water seepage into the ground is not interfered with significantly.
A problem with the present interlocking blocks, however, is that they are cement based and therefore somewhat porous. This means that they can absorb moisture which tends to cause them to crack or break when the moisture freezes during winter weather conditions.
Although some prior art paving blocks, particularly those that are cement based, are available in a variety of colours, there is no known prior art that provides both the structural aspects of an asphalt based block which also includes plastic, rubber and the like, with the aesthetic features of other blocks, or with the aesthetic features and functional features of other materials not normally incorporated into paving blocks. For instance, at the present time, it is generally not possible to match asphalt based paving blocks to the colour of different types of building materials such as bricks, granite, natural stone, and the like. Nor is it possible to provide a paving block having a top surface including materials that are chosen only for their aesthetic properties or for their frictional or tractional properties, or for their cushioning properties but not for their structural properties. All known paving blocks are made of a single mixture that is relatively homogenous in consistency, the components of which must generally be chosen for their structural properties. It is not known to provide a paving block having a separate layer that exhibits aesthetic and mechanical properties that are different than the aesthetic and mechanical properties of the main structural layer or body of the paving block. Further, it is not known how to produce such a two layer block wherein the two layers are bonded with one another so as to form a securely interlocked structural seam therebetween.
Presently, many situations exist where present paving solutions, including interlocking blocks, are not completely satisfactory. In parking lots, for instance, cement based paving blocks may be used, but are generally not suitable as they are not rugged enough to withstand the rigour of parking lot traffic, including heavy trucks, and also snow ploughs during the winter months. Alternatively, asphalt based paving blocks can be used. However, use of strictly asphalt paving blocks would result in a black colour parking lot. While a black colour parking lot is generally acceptable, it may be desirable to have another colour available. This is especially true where other paved surfaces are concerned, such as driveways, patios, playgrounds, and so on.
What is required is an asphalt based paving block having a second top layer containing materials other than asphalt, wherein this top layer may be any suitable colour. Further, the top layer may include materials having specific properties that are desirable in specific situations. Suitably manufactured paving blocks could have a top layer that has a specific resistance to oil and salt, for example.
Such two layer paving blocks could be used to outline specific areas of a parking lot or to provide the lines between parking spaces. Further, two layer paving blocks could also be used to provide the dividing lines on public roads and the "stop lines" at intersections, and the like.
Public roadway intersections, which are known to be prone to being slippery during rainy weather due to the amount of oil that has dripped from cars could have blocks having a top layer that has very high traction characteristics so as to allow for reduced stopping distances even in slippery conditions.
Materials that are sensitive to temperature and that change colour in response to changes in temperature, could be used to indicate when temperatures are around freezing and driving conditions might be slippery.
Paving blocks having increased sound absorbency characteristics could be used on downtown city streets.
Paving blocks having a somewhat soft top layer could potentially be used playgrounds to provide a top surface having relatively high physical cushioning properties.